There are two types of water heaters in widespread use; viz.: the instantaneous water heater and the batch water heater. The first category of heaters, also known as continuous flow heaters, is exemplified by the water heaters disclosed in U.S. Pat. Nos. 4,424,767 and 4,282,421. They typically include a small vessel or pipe with no substantial storage capacity and a high capacity heat source activated by the flow of water and/or a thermostat. Continuous flow water heaters provide hot water only on demand, thus eliminating standby losses.
However, the known prior art continuous flow water heaters are significantly limited in flow deliver capacity by the heat input available. The heating rate capacity of electric heaters is determined by the available wattage of the elements (five to seven kilowatts typically) and by the available electrical service (typically thirty amperes maximum). These factors restrict the available hot water temperatures to less than satisfactory levels for the continuous flow requirements of most users. Another disadvantage of the prior art continuous flow water heaters is their inability to accurately regulate the output temperature as flow rates fluctuate without the use of expensive and complex controls. Still another disadvantage of the prior art water heaters of this class is that the heating element is usually built-in and is therefore not replaceable. As a result, failure of the heating element alone necessitates replacement of the entire heater unit. The present invention addresses and solves these and other problems characteristic of the prior art continuous flow water heaters.
It would be highly advantageous, therefore, to overcome the deficiencies of the existing continuous flow water heaters presently available.